This study focuses on the solid oxide fuel cell (SOFC) cogeneration system for commercial buildings. SOFCs are considered to be suitable for buildings with low thermal demand because of the high power generation efficiency. The objective of this study is to analyze the effects of SOFC installation into various commercial buildings from energy saving and economic aspects using optimization minimizing the system cost. Primary energy reduction rate was used as the indicator of the energy saving performance. The results showed that SOFCs are effective to reduce primary energy consumption for all the buildings analyzed in this study. Based on the analysis of the optimal installation, it is suggested that SOFCs economically perform better for the buildings such as hospitals, hotels and restaurants with hot water demand than for offices without hot water demand. Restaurants operating for 24 hours are expected to be a promising candidate of SOFC, which can accept the cost of SOFC as high as 1.05 million yen per kilowatt. Furthermore, sensitivity analysis on the effects of SOFC installation based on renewable energy levy showed that installation of SOFCs would be promoted strongly for buildings with high electricity demand.

In order to improve the compressor cycling stability and hydrogen storage properties of V₄₀Ti_21.5Cr_38.5 alloy further, the fourth element i.e. Niobium, Iron, or Zirconium has been substituted for Cr to prepare V₄₀Ti_21.5Cr_33.5M₅ alloy and their cyclic hydrogen absorption-desorption performance was evaluated up to 100 cycles for temperature and pressure ranges of 20-300 °C and 5-20 MPa, respectively. All the three compositions have shown different sorption properties as well as cyclic stability. The V40Ti21.5Cr33.5Nb5 alloy was found a most suitable composition with a comparatively high hydrogen capacity and reasonable stability after 50 cycles of compressor cyclic test, whereas, V₄₀Ti_21.5Cr_33.5Fe₅ alloy has shown worst cyclic stability with lowest hydrogen capacity. However, structural and morphological investigations suggest no phase segregation during the cycling of V₄₀Ti_21.5Cr_33.5Fe₅ alloy in contrast to the other alloys, which suggest that phase segregation is not the only responsible reason for the performance degradation of BCC alloys employed for compressor cycle. In some cases similar to V₄₀Ti_21.5Cr_33.5Fe₅, stress/strain formation in the lattice during cycling may also cause the degradation of the material.

Oxy-fuel IGCC is developed as a CO₂ recovery type power generation system with high thermal efficiency. In order to verify O₂/CO₂ blown gasification process applied to the oxy-fuel IGCC, O₂/CO₂ blown gasification tests were conducted with a coal throughput of 50 tons per one day (50 t/d) scale for the first time. It was confirmed that slag discaharging characteristics was smooth and that the gasifier can be operated stably under O₂/CO₂ blown conditons. As a result of measurement of major syngas components, it was shown that the performance of 50 t/d gasifier can be predicted by existing simulation method. Hydrocarbon measurement in the syngas was carried out in O₂/CO₂ blown gasification, and it was suggested that the amout of hydrocarbon can be adjusted by tuning the operating parameters. Furthermore, applicability to a commercial scale oxy-fuel IGCC system was examined by applying the simulation confirmed in the gasification test.